1. Field of the Invention
The present invention relates to an oil pump resonator in which various vibrations caused by pulsations that change in response to changes in oil pressure on a discharge port side can be attenuated by a resonator that comprises only one chamber, whereby the volume occupied by the resonator can be minimized.
2. Description of the Related Art
Means for reducing pump discharge pulsations in oil pumps comprising an internal gear structure such as a rotor or thelike provided in a pump housing, include, for instance, forming a portion, called a resonator, at a discharge port or midway along a discharge flow channel that communicates with the discharge port. The resonator comprises a communicating channel that communicates with the discharge port, and a chamber (a space of given volume). The pulsations entering the chamber of the resonator are reflected into pulsations having exactly a reverse phase of the pulsations that travel along the flow channel, as a result of which these pulsations traveling along the flow channel are cancelled. This allows reducing pulsations of a specific frequency range. During driving, therefore, the driver experiences no discomfort arising from gradually increasing vibration and noise, perceptible by the driver, as engine revolutions increase.
In actuality, however, there may exist resonance point at any site or location. There exist also at a plurality of points resonance frequencies for which pulsations increase peak-like at specific frequencies. When the above pulsation peaks exist, first of all vibration and noise perceptible by the driver do not change smoothly in response to changes in revolutions, and hence the driver experiences discomfort during the driving operation. Secondly, the pulsation peak values at resonance frequencies are far larger than the magnitude of the pulsations at other frequencies. The presence of pulsation peak values, therefore, drives up considerably the overall magnitude of pulsations. Such peak frequencies, moreover, do not occur at one single point, but at plural sites. Japanese Patent Application Laid-open No. 2007-16697, for instance, discloses a method for reducing pulsation peaks of plural frequencies.
The frequencies of the pulsations that the resonator is capable of reducing can be adjusted on the basis of the volume of the resonator. More specifically, a resonator having a larger volume allows reducing pulsations of lower frequencies, while a resonator having a smaller volume allows reducing pulsations of higher frequencies. Such being the case, Japanese Patent Application Laid-open No. 2007-16697 provides a plurality of oil chambers, of dissimilar volume, communicating with a discharge channel of an oil pump, making it possible thereby to reduce pulsations of frequencies identical to those of the oil chambers.
However, the oil pump in Japanese Patent Application Laid-open No. 2007-16697 has the following problems. Firstly, it is necessary to provide as many oil chambers as there are frequency points for which pulsations are to be reduced. In case of multiple frequencies for which pulsations are to be reduced, however, providing multiple oil chambers may be impossible in practice, in terms of engine layout, while there are obvious limits to the number of oil chambers that can be arranged. Secondly, the volume occupied by the plurality of oil chambers that must be arranged becomes extremely large (oil chamber volume×number of chambers). Thirdly, although pulsations can be reduced for a number of frequency points corresponding to the number of oil chambers that are provided, the frequencies that can be reduced are point frequencies, and thus pulsations of frequencies deviating from these points cannot be reduced.